1. Field of the Invention
The present invention relates to optical layered products to be provided on display surfaces of liquid crystal displays (LCDs), plasma displays (PDPs) and the like and, in particular, to optical layered products for improving visibility of screens.
2. Description of the Prior Art
Recently, displays such as LCDs and PDPs have been improved to be produced and sold in various sizes for a number of applications ranging from mobile phones to large-size television sets.
Such displays may have impaired visibility due to background reflections into the display surfaces of room lightings such as fluorescent lights, sunlight incident through windows and shadows of an operator. As such, in order to improve visibility, the display surfaces are provided with functional films on the outermost surface, such as antiglare films having microirregularities, which are capable of diffusing surface-reflected lights, suppressing specular reflections of external lights and preventing background reflections of outside environments (having antiglare properties) (conventional AG).
These functional films are generally produced and sold as products comprising a translucent substrate such as polyethylene terephthalate (hereinafter referred to as “PET”) and triacetyl cellulose (hereinafter referred to “TAC”) over which an antiglare layer having microirregularities is provided or as products comprising a light-diffusing layer on which a low-refractive index layer is layered, with development now being carried out for functional films providing desired functions through combinations of layer configurations.
With a recent progress of an increase in size, definition and contrast of displays, however, there is now a need for enhancement of performance required for such functional films.
When an antiglare film is used for the outermost surface, images in black tend to be whiter due to diffusion of light with a disadvantageous decrease in contrast for use in a bright room. An antiglare film is therefore needed which attains a high contrast even at the sacrifice of antiglare properties (high-contrast AG).
In order to attain a high contrast, a method has been adopted in which one or more low-reflection layers are provided onto the top layer of an antiglare film (AG with low-reflection layer).
On the other hand, when an antiglare film is used on the outermost surface, a problem arises in which dazzling (portions with high and low intensities in brightness) appears on the surface supposedly due to the microirregularities, decreasing visibility. Such dazzling is likely to occur in association with an increased definition in association with an increase in number of picture elements for a display and with improvement of display techniques such as picture element division scheme. An antiglare film having an antidazzle effect is therefore desired (high-definition AG).
In order to attain antidazzle effects, development is ongoing for a method as in Patent Reference 1, in which Sm (average peak spacing), Ra (center line average roughness) and Rz (average ten-point height of irregularities) of the surface of functional films are specifically defined and for a method for regulating background reflection of external lights into a display screen, dazzling phenomenon and white balance as in Patent References 2 and 3, in which areas of surface haze and internal haze are precisely defined. As such, in designing a light-diffusing sheet to be used for high-definition LCDs, internal diffusion properties for providing antidazzle effects and surface diffusion properties for providing antiwhitening effects are controlled.
Patent Reference 1: Japanese Unexamined Patent Publication No. 2002-196117
Patent Reference 2: Japanese Unexamined Patent Publication No. 1999-305010
Patent Reference 3: Japanese Unexamined Patent Publication No. 2002-267818
Thus, there are problems to be solved such as antiglare functions, contrast enhancement and antidazzling and there is a tradeoff in which one of the properties can be sought only at the sacrifice of the others. Nothing so far has satisfied these functions with a configuration where a single layer is layered on a translucent substrate. As such, as a method for providing these functions simultaneously, development is under way with respect to the shape of membranes and films to be coated in a multi-layer manner. Such multi-layer lamination however requires a process for coating a translucent substrate with multiple layers, incurring more cost. Also, it is difficult to adjust the balance between the multiple layers, only allowing in fact to select and implement part of these functions according to the intended use.